Debt review that I did not ask for

If you receive an unsolicited call from Financial Debt Advisors / FDA / Hyphen PDA in which they offer to reduce your monthly debt repayments, HANG UP! I was sucked into a debt review application over the phone that it turns out I did not need (as I can afford my debt). As soon as they sent me the paperwork, I read through it, changed my mind about the application and asked for it to be cancelled. I was told that, because I had rep**** "Yes" to one of their many WhatsApp messages, they had the right to submit the application to my creditors before I had received the paperwork, so I would have to pay them a R300 cancellation fee. I'm now under debt review, and my credit score has been negatively affected.